This proposal is directed toward studies of color perception with the overall goal of relating man's color perception in the natural world to laboratory studies of color vision under reduced stimulus conditions. To achieve this goal three approaches will be used. l. Psychophysical studies will compare color discrimination and color appearance using stimuli specified by their cone excitation. The effects of chromatic surrounds on chromatic discrimination will be measured. The same stimulus arrays will be used to assess equilibrium colors and color appearance of the arrays will be assessed by asymmetric matching in the haploscope. Chromatic bar patterns will be used to investigate the effects of spatial parameters on induction and assimilation. Adaptation in both luminance and chromaticity will be controlled and manipulated. For each display, discrimination will be measured and appearance will be assessed by haploscopic matching using the same observers and carefully controlled adaptation. 2. The data of the experiments will be compared to a model of chromatic discrimination based on knowledge of neural processing (spectral opponency). The preliminary version of the model is based on data collected during the previous grant period. A goal of the new proposal is to develop a physiological model of early color processing incorporating both adaptation and chromatic discrimination. The ultimate model will incorporate a computational approach to chromatic discrimination signals (i.e. how the color system adapts to the time average chromaticity and luminance). 3. The discrimination data and model fits will provide a description of the input signals reaching later processing stages. The models can also predict expected equilibrium colors and color appearance based on the early spectral opponency. The divergence of measured equilibrium colors and color appearance from that predicted on the basis of the early adaptation signals will form the basis to establish what needs to be incorporated in later stage descriptions of color appearance.